'Does E still equal MC squared?'

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"Does E still equal MC squared?" So asks the Irish band the Corrigan Brothers in a new song, 'Einstein and the Neutrinos', that is the latest rollicking riff on news that shocked the scientific world last month. A group of physicists from Italy claimed they had observed the sub-atomic particles called neutrinos traveling faster than the speed of light. That, of course, is the cosmic speed limit declared in Albert Einstein's theory of special relativity in 1905.

If they are right - and the jury is still out - Einstein might have some explaining to do. Among other things, a neutrino or anything else that went faster than the speed of light could go backward in time. Physicists, who are quite sure that in fact E does still equal MC squared - whatever may come of this experiment - have expressed skepticism. But that has not stopped the ghostly neutrinos from achieving a sort of pop culture fame not seen since 1960, when John Updike published a poem about them in The New Yorker: The Earth is just a silly ball To them through which they pass Like dustmaids down a drafty hall Or photons through a sheet of glass.

Neutrino time-travel jokes have proliferated on the internet. Example: "We don't serve faster-than-light neutrinos here, " said the bartender. A neutrino walks into a bar. Under a YouTube video of the Corrigan Brothers (who played at President Obama's inauguration ), one commenter observed: "Irish Folk & particle physics - what a combo. "

The neutrino news came from a group of physicists based at the Gran Sasso underground laboratory in Italy and doing business under the apt acronym Opera. The neutrinos, they reported on September 23 in a paper and at a special symposium at CERN, the European Centre for Nuclear Research, had beaten a metaphorical light beam from CERN to Gran Sasso, a distance of 457 miles, by 60 nanoseconds. The initial response of physicists assembled at CERN and around the world was that there was probably a mistake somewhere in the experiment. Einstein's theory is the basis of all modern physics, and has been tested a zillion times. "It looks too big to be true, " Alvaro de Rujala, a CERN theorist, said at the time. Or as the Corrigan Brothers put it: Was old Albert wrong? Oh can it be, that fabulous theory - relativity - is being debunked for the first time? But he still might be right, old Albert Einstein. Physicists, in the meantime, have been flooding arXiv. org, the physics internet archive, with papers debunking the Opera experiment and defending Einstein. In one paper, two professors from Boston University, Andrew G Cohen and the Nobelist Sheldon L Glashow, showed that if the neutrinos had been going faster than light en route to Gran Sasso, they would have lost energy at a fearsome rate by emitting other particles, causing distortions in the beam that were not seen by Opera. Another paper - by Gian Giudice of CERN, Sergei Sibiryakov of the Institute for Nuclear Research in Moscow and Alessandro Strumia of the University of Pisa in Italy and the National Institute of Chemical Physics and Biophysics in Tallinn, Estonia - argued that according to the Standard Model, the reigning theory in particle physics, if neutrinos could violate relativity, electrons should violate it also, something that has also not been observed.

Last week, in what sounded like the coup de grace in some circles, Ronald A J van Elburg, an artificial intelligence researcher at the University of Groningen in the Netherlands, suggested that the Opera group had failed to make a relativistic correction for the motions of the GPS satellites used in timing the neutrino beams. The resulting error, he said, amounted to 64 nanoseconds, almost exactly the universe-shaking discrepancy the Opera researchers were hoping to explain.

That paper got wide attention. It was mentioned on a physics blog of the magazine Technology Review, and was published by the Massachusetts Institute of Technology and other news sites as a possible explanation of the neutrino mystery. "If it stands up, this episode will be laden with irony, " Technology Review wrote. Far from breaking Einstein's relativity, it went on, "the faster-than-light measurement will turn out to be another confirmation of it. " The Opera collaborators and other outside physicists now say Dr van Elburg's analysis is wrong.

Reached in Groningen, Dr van Elburg said that an improved version of his manuscript was now under peer review. John Learned, a neutrino physicist at the University of Hawaii, wrote in an email that while the Opera results might not be right, "they are still not easily dismissed. " "It is very unlikely to me that any distant observer will point out the error of their ways, " he continued. "If a screw-up, it is probably in the details not accessible to outsiders. "

Meanwhile, Halloween is almost here. Don't be surprised if you have already seen Einstein in a neutrino costume.